This may sound like a stupid question, but as I was looking for aftermarket lower receivers for the LM4 I realized there really are none, and so I started looking at real steel lower receivers and the possibility of using one with the LM4. Though I know next to nothing about AR-15s, I was looking on the internet and the two rifles, both real and airsoft, seem to have very similar parts housed in the lower receiver. So do you think it would be possible to incorporate a real steel lower receiver on an LM4 with little to no modifications or not?

The area where the upper lugs meet the lower are narrower in the M4 (the sides are thicker and stronger) and the magazine well and catch only vaguely match. The trigger group is entirely different, etc.

Yep, you can buy a bare AR15 lower for about $70 many places but you're not going to get your LM4 upper to fit on it.